1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and a designing method therefor; more particularly, to a semiconductor integrated circuit formed of a semiconductor chip having input/output cells arranged only along two sides thereof facing to each other and to a designing method therefor.
2. Description of the Related Art
There is a known technique for increasing the number of input/output cells arrangeable on a semiconductor chip of a semiconductor integrated circuit which is formed of the semiconductor chip having input/output cells arranged along an outer periphery thereof. For example, Japanese Unexamined Patent Application Publication No. Hei 4-56355 has disclosed a semiconductor integrated circuit in which a power supply line has linear portions on input/output cells arranged along an outer periphery of a semiconductor chip and curved portions along corners of the semiconductor chip. The curved portions of the power supply line are smaller in width than the linear portions and are formed in multilayers. This makes it possible to form the input/output cells also in areas near the corners of the semiconductor chip. As a result, a larger number of input/output cells can be arranged on the semiconductor chip.
Further, Japanese Unexamined Patent Application Publication No. Hei 5-48048 has disclosed a semiconductor integrated circuit in which four input/output cell areas are formed by arranging input/output cells outside a basic cell area in parallel with each of four sides surrounding the basic cell area. A corner area of two joining sides is shared by two input/output cell areas, and input/output cells forming one of the input/output cell areas are arranged therein. A metal power supply line on one of the input/output cell areas does not have any connecting terminal to electrically connect to a metal power supply line on the other input/output cell area. Such a configuration enables efficient arrangement of a large number of input/output cells on a semiconductor chip.
In case of a semiconductor integrated circuit having a small number of input/output cells (namely, external input/output terminals), the input/output cells are often arranged only along two sides of a semiconductor chip facing to each other due to easiness in terms of manufacturing or the like. However, Japanese Unexamined Patent Application Publication Nos. Hei 4-56355 and Hei 5-48048 have disclosed a technique for forming a semiconductor integrated circuit with a semiconductor chip having input/output cells arranged along all the four sides thereof, but not one with a semiconductor chip having input/output cells arranged only along two opposite sides thereof.